Studies of Soil Erosion Using Isotop (137Cs and 210Pb excess) at Ciesek Sub Watershed, Upper Ciliwung Watershed, Bogor | Kajian Erosi Tanah menggunakan Isotop 137Cs dan 210Pb Excess di Sub DAS Ciesek, DAS Ciliwung Hulu, Bogor

indonésien. Metode jatuhan radioisotop (Fallout Radio Nuclides) telah lama dimanfaatkan dan dikembangkan untuk mempelajari dan mengukur erosi tanah. Penelitian ini bertujuan menduga erosi/deposisi tanah di Sub DAS Ciesek, DAS Ciliwung Hulu menggunakan jatuhan radioisotop 137Cs dan 210Pb excess di alam. Pengambilan sampel tanah dilakukan menggunakan soil core pada empat transek penggunaan lahan yang berbeda. Sampel tanah dianalisis menggunakan Multi Channel Analyzer (MCA) untuk mendapatkan nilai inventori kedua radioisotop tersebut. Hasil penelitian menunjukkan perbedaan pola distribusi erosi/deposisi antara isotop 137Cs dan 210Pb excess. Penggunaan isotop 137Cs menunjukkan proses erosi tanah terjadi pada lahan kebun campuran dan tegalan, tapi proses deposisi terjadi di lahan terbuka. Penggunaan 210Pb excess menunjukkan erosi tanah terjadi di lahan terbuka, namun deposisi terjadi di lahan kebun campuran dan tegalan. Penggunaan 210Pb excess pada penelitian ini lebih dapat diandalkan dibandingkan dengan 137Cs, dalam hal pendugaan erosi tanah

anglais. Fallout radio nuclides method has been being applied and developed to study and measure soil erosion for long time. This research aims to predict soil erosion/deposition in Ciesek subwatershed, Upper Ciliwung watershed using natural fallout radionuclides of 137Cs and 210Pb excess. Soil samples were taken using soil core along four transects of different land use types.  Soil samples were analyzed using Multi Channel Analyzer (MCA) to obtain inventory value of the radioisotopes. The research shows different distribution pattern of soil erosion/deposition of 137Cs and 210Pb excess isotopes. Application of 137Cs isotope shows soil erosion process under home mix garden and dryland farm, but soil deposition process occurs on bareland. In the contrary, 210Pb excess indicates soil erosion on bare land while soil deposition is under home mix garden and dryland farm. Application of 210Pb excess is more reliable than 137Cs in predicting soil erosion.